Not Applicable
Not Applicable
This application is a continuation and expansion of Provisional Patent Application No. 60/249,435, Nov. 17, 2000.
Conventional ground penetrating radar (GPR) surveys are generally conducted by moving the radar antennas over the surface of the underground medium of interest along a prescribed grid pattern while taking a continuous series of radar xe2x80x9cphotographsxe2x80x9d directly into the ground. These data are subsequently processed and integrated into composite cross-sectional displays of the underground, from which profiles of various geologic features can be discerned, and anomalies (i.e., discontinuities in an otherwise homogenous volume, or xe2x80x9ctargetsxe2x80x9d) can be pinpointed.
Application of this GPR exploration technique in confined underground spaces, such as the tunnels of hard-rock mines, is not possible simply because of the rough and irregular nature of such tunnels and also because of the need to prevent the radar waves from reverberating off the tunnel walls and creating a jumble of false targets. These considerations require that the radar searches be conducted at successive smoothed sites along the walls of the mine, with the results being integrated in some fashion, or the development of the data received from a single direction, utilizing a method such as that described in referenced U.S. Pat. No. 6,091,354, or the use of a wideangle scanning system such as that presented in this application.
The present GPR invention utilizes a wide-angle view seen through a chosen xe2x80x9cwindowxe2x80x9d in the rock surface, which view is divided into some 300 narrow-angle xe2x80x9cpixelsxe2x80x9d. The data from each pixel is independently processed and recorded, and the 300 sets of data (or waveforms) are then integrated into detailed displays of the interior of the underground in any of several formats: a wide-angle face-on display of the entire scene; a range-gated face-on display to enable study of successive layers of the wide-angle scene; a slice across the center of the scene, at any angle, for offset plan-position displays; an A-scan display of any individual pixel; or a transparent 3-D display which may be rotated at will.
The features described in the foregoing paragraph are drawn from modem radar systems (e.g., airport radar; surveillance radar; gun control radar; etc.) but are features not hitherto utilized in GPR systems because of the inability of available GPR systems to scan the interior of the rock walls of a mine from one selected site. It is the unique antenna-scan system being introduced herein that allows the GPR user to incorporate these proven and very valuable techniques. It should be re-emphasized that these types of displays made available to the GPR user allow the user to obtain, in addition to direction and distance to any and all targets, an indication of the size and orientation of those targets and valuable information as to the geologic structure within the volume being surveyed.
The heart of the present invention is the unique antenna system with which important operational capabilities of conventional radars are now made available to users of ground penetrating radar (GPR) systems. Specifically, this antenna system consists of a hemispherically shaped dome, having the same relative dielectric constant (ER) as that of the medium to be surveyed, which is placed against a flattened portion of that medium, and a microwave horn antenna which is placed against that hemispheric dome so as to transmit through the dome and into the medium of interest, and a means of moving that horn antenna over the spherical surface of the dome and thus directing the beam of the antenna throughout the conical volume thus made available. The horn itself may be fully dielectrically xe2x80x9cloadedxe2x80x9d, allowing its dimensions to be reduced, or may utilize a concave-convex lens (in air dielectric horns, if used) to correct for the close-in focusing effect of the dome itself.
The preferred antenna system may be as depicted in FIG. 6 and FIG. 7 where-in a horn antenna is fitted with a reflector, and a scanning method selected which is relatively easy to implement. In this instance the horn antenna is fully loaded with a dielectric material which has an ER substantially equal to that of the material being surveyed, allowing the total size of the horn-reflector assembly to be much smaller and the radar housing kept to a minimum size. Lensing is not a factor in this design.